Manufacturing motors in the price competitive market is accomplished as inexpensively as possible balanced against quality of structural components for satisfactory performance during a reasonable life span in turn balanced against the selling price of the motor.
One of the basic cost considerations is the cost of bearings and the still larger cost of mounting them. In electric motors, for example, the usual thrust imposed on the drive shaft is in a radial direction because most of the loads imposed on the drive shaft are pulleys which drive belts, saws, etc. Thus the motors are equipped with radial thrust bearings which adequately support radial loads. These radial bearings will support some axial load for short periods, but, when they are operated under axial load for long periods, the radial bearings are insufficient to support the axial load for the same use period as the radial bearings will support a radial load. Usually the imposition of an axial load causes the radial thrust bearings to wear out very quickly requiring replacement of the motor.
Since the integration of axial thrust bearings in a motor is expensive and since in most uses the motors only support radial loads, the manufacturers do not find it economically justified to equip all the motors with axial thrust bearings when they would usually not be used.
However, when a purchaser buys a motor only equipped with radial thrust bearings and imposes an axial load on it for a period and it quickly wears out, he has lost his investment, has to go to the expense of replacing the motor, and if he does not buy a more expensive motor with axial thrust bearings, the same failure happens again.